docs: def ast_str(self, indent=0):
          """Return a minimal string to print a tree-like structure.
  
          Kwargs:
              indent (int): The number of indentation levels.
          """
          line = self.line or 0
          col = self.column or 0
          name = type(self).__name__
          spell = getattr(self, 'name', '[no spelling]')
          result = ' ({})'.format(self.result) if hasattr(self, 'result') else ''
          prefix = indent * '| '
          return '{}[{}:{}] {}{}: {}'.format(prefix, line, col,
                                             name, result, spell)